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Kinetics of cation ordering in natural Mg(Al,Cr3+)2O4 spinels
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F. Princivalle
Veröffentlicht/Copyright:
31. März 2015
Abstract
The kinetics of cation ordering (quench method) in two natural Mg(Al2-yCry)O4 spinels (y~ 0.03-0.06 and 0.24), highly ordered in terms of Mg-Al, were studied by means of X-ray single-crystal diffraction. The equilibrium distribution of Mg and Al between tetrahedral and octahedral sites was investigated at 650 °C (in disordering and ordering) and at 850 °C (in ordering), through several time-steps to monitor the rate of cation distribution before equilibrium was achieved. The cation distributions for both disordering and ordering experiments were obtained by measuring the oxygen positional parameter u, which is correlated to the inversion parameter x (Al in T site), and then to the composition of the samples.
The Mueller kinetic model, satisfactorily applied to the experimental data, allowed the calculation of the kinetic ordering constants K, linearly related to temperature by means of Arrhenius equations.
The kinetics of ordering processes are influenced by Cr content. The equilibrium for both the isotherms at 650 and 850 °C was reached at different elapsed times by the low- and high-Cr spinels: the time for the low-Cr sample was, in both the ordering experiments, about double that of the high- Cr sample. Consequently, the activation energy (186 and 175 kJ/mol for low- and high-Cr samples, respectively) for the intracrystalline Mg-Al ordering decreases with Cr increase.
Received: 2005-1-11
Accepted: 2005-6-17
Published Online: 2015-3-31
Published in Print: 2006-2-1
© 2015 by Walter de Gruyter Berlin/Boston
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Artikel in diesem Heft
- Presidential Address: Elastic properties of minerals and the influence of phase transitions
- Pressure-induced hydration in zeolite tetranatrolite
- Annealing experiments on induced fission tracks in apatite: Measurements of horizontal-confined track lengths and track densities in basal sections and randomly oriented grains
- Alpersite (Mg,Cu)SO4·7H2O, a new mineral of the melanterite group, and cuprian pentahydrite: Their occurrence within mine waste
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- Hydrogen incorporation in olivine from 2–12 GPa
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- Thermodynamics and kinetics of cation ordering in natural and synthetic Mg(Al,Fe3+)2O4 spinels from in situ high-temperature X-ray diffraction
- Kinetics of cation ordering in natural Mg(Al,Cr3+)2O4 spinels
- Equations of state and structures of andalusite to 9.8 GPa and sillimanite to 8.5 GPa
- Equation of state and phase transition in KAlSi3O8 hollandite at high pressure
- A novel arrangement of silicate tetrahedra in the uranyl silicate sheet of oursinite, (Co0.8Mg0.2)[(UO2)(SiO3OH)]2(H2O)6
- Aluminum substitution in stishovite and MgSiO3 perovskite: High-resolution 27Al NMR
- The effect of chlorine on the viscosity of Na2O-Fe2O3-Al2O3-SiO2 melts
- TEM imaging and analysis of microinclusions in diamonds: A close look at diamond-growing fluids
- A partial molar volume for ZnO in silicate melts
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- The crystal structure of a second antigorite polysome (m = 16), by single-crystal synchrotron diffraction
- Oxide melt solution calorimetry of sulfides: Enthalpy of formation of sphalerite, galena, greenockite, and hawleyite
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